A technique of observing the earth's surface from an aerial position (far from an observed object) by an observation device installed in an artificial satellite, an aircraft, or the like is generally referred to as remote sensing. In the remote sensing, an intensity of an electromagnetic wave such as light, which is radiated from a predetermined area on the earth's surface, is often observed.
In observation by the remote sensing, one observation value is often stored as a pixel value associated with a pixel. The pixel is one of a plurality of pixels constituting an image (observation image). For example, each of the observation values with respect to each point or each small area included in a predetermined area on the earth's surface is stored as the pixel value of the pixel associated with the point or the small area on the observation image. In this case, the observation image is an image in which each of pixels located at each position according to each point or each small area of the predetermined area holds the observation value. The observation value is obtained by observing an electromagnetic wave radiated from the earth's surface within the predetermined area. Note that, in the observation image, the pixel value is a value of the pixel located at a position depending on a position on the earth's surface within an observed area. Therefore, it may be said that each pixel value included in the observation image represents the observation value (such as the intensity of the electromagnetic wave radiated from each position) with respect to each position depending on the position on the earth's surface within the predetermined area.
In particular, when the observation device includes an image sensor, an observation result is often obtained in a form of image. In this case, the pixel value of each pixel included in the observation image may be a value (observation value) that represents an intensity of light incident on a light receiving element of the image sensor. The observation value includes information on light radiated from the earth's surface or the like and incident on the light receiving element of the image sensor. Note that the image sensor is also referred to as an imaging element, and the observation device is also referred to as an imaging device. In this case, the observation image is also referred to as a captured image. Further, in the following, the light radiated from the earth's surface and observed by the observation device may be referred to as observation light. When the observation device includes the image sensor, more specifically, the observation light is light incident on the light receiving element of the image sensor.
In addition, when the pixel value is a value representing brightness for each observed wavelength band, the value (the pixel value) representing the brightness is also expressed as a luminance value. The observation device may observe light of a specific wavelength included in a wavelength band of a specific range. For example, using a filter for selectively transmitting light of the wavelength included in the wavelength band of the specific range, the observation device is able to limit the wavelength band of the observation light. Further, using a plurality of filters having different light transmission wavelength bands, the observation device is able to obtain, as an observation result, an intensity of the observation light for each transmission wavelength band of the filter.
The observation image obtained as described above is used for various purposes such as discrimination of an object covering the earth's surface, observation of a state of the earth's surface, and the like, or is expected to be used. For example, as an application by which use of the observation image as described above is expected, farming support, searching for resources, and the like are exemplified. More specifically, an application of acquiring a state or a material of the covering object on the earth's surface, based on information on a surface reflectance of the covering object included, as the pixel value, in each pixel of the image obtained by remote sensing, and performing farming support, searching for resources, and the like, is expected. For example, in farming support and searching for resources, it is expected to acquire growth of crops or to discriminate minerals captured in the observation image, with use of the observation value held in the pixel of the observation image.
However, in order to obtain accurate information on the state of the earth's surface or the covering object on the earth's surface (e.g. crops, ores, and the like) from the observation image, it is necessary to estimate a component depending on an environmental condition, and to correct the observation value (pixel value). PTL 1 discloses a technique relating to technique of eliminating unnecessary information from the observation image, and extracting only necessary information. Further, PTL 2 discloses a technique of correcting image data such as an aerial image or a satellite image.